1. Field of the Invention
This invention relates to a technique for recording information on an optical disc using a laser beam or other means.
2. Description of Related Art
Onto a recordable or rewritable optical disc such as a DVD-R (DVD-Recordable) or a DVD-RW (DVD-Rerecordable), information is recorded by irradiating a laser beam on its recording surface. At the areas on the recording surface of the optical disc where the laser beam is irradiated, the property of the optical recording medium forming the optical disc is physically changed because of the increased temperature. This produces recording marks on the recording surface.
Namely, the laser beam is modulated by recording pulses having time widths corresponding to information to be recorded, so that the laser pulses having lengths corresponding to information to be recorded are generated and irradiated on the optical disc. Thus, recording marks having lengths corresponding to the information to be recorded can be formed on the optical disc.
One approach recently used is to form a recording mark by a pulse train having a plurality of short pulses, rather than by a single laser pulse. This approach, called “write strategy”, introduces less heat accumulation on the recording surface of the optical disc compared to the approach irradiating a single recording laser pulse. Therefore, uniform temperature distribution can be achieved on the recording surface on which the recording marks are formed. This can prevent undesired teardrop-shaped recording marks from being formed, and enables the formation of the recording marks of preferred shape.
In the case of DVD-R, for example, the recording pulse train consists of a plurality of pulses which magnitude varying between a read power level and a write power level. That is, based on recording data, the areas on the recording surface of the optical disc where no recording marks are to be formed (referred to as “space periods” hereafter) are irradiated with the laser beam of the read power. The areas on the recording surface of the optical disc where recording marks are to be formed (referred to as “mark periods” hereafter) are irradiated with the laser beam of the power corresponding to the recording pulse train having magnitudes varying between the read power and the write power. Consequently, the recording marks are formed on the recording surface. In the case of DVD-RW, the recording pulse train has a waveform with amplitudes varying between four power levels: the read power level, an erase power level for erasing the recorded mark already formed, the write power level, and a cooling power level (typically equal to the read power level).
Such discs are manufactured by various manufacturers and have different characteristics on a manufacturer basis or even a product basis. Therefore, there are differences in optimum recording power and write strategy used in recording information between the discs. Generally, each disc has information on the recording power and the write strategy reflecting its own characteristics (hereafter referred to as “recording condition information”), which is considered to be optimum. In one approach, this recording condition information is included in LPP (Land Pre-Pit) information and recorded on the disc as the LPPs. In another approach, the recording condition information is stored in a microcomputer of a recording apparatus. In this case, a manufacturer ID is recorded on the disc, whereas the recording condition information is stored in the microcomputer of the recording apparatus in association with the manufacturer ID. Thus, when the recording apparatus records information on the disc, it reads out the recording condition information in the LPP information or retrieves the recording condition information corresponding to the manufacturer ID recorded on the disc from the microcomputer in itself, and then records the information according to the recording condition information. This allows the information to be recorded under the recording condition recommended by the disc manufacturer or the like.
While these approaches to determine the recording condition allow information to be recorded substantially properly on a disc when the disc has a sufficiently wide margin (tolerance) in its characteristics, the quality of actually recorded signals still varies to some extent. This results from variations in each information recording apparatus, such as an error in laser power adjustment and the pulse emission characteristic during recording, or variations in characteristics of each disc. If the recording speed further increases in the future, the margin in characteristic of the disc, that is sufficiently wide for a normal recording speed, will be relatively narrow, so that proper recording may become difficult or impossible. In addition, discs with various characteristics manufactured by different manufacturers will be commercially available as DVD-RW becomes popular. Some of the discs may have a narrow margin, and it is quite possible that the proper information recording is not ensured for such discs.